I have many reasons to smoke alone:

1. my age and occupation - I need to be secretive.
2. nobody else I know smokes and most would disapprove heavily.
3. it's my time to unwind, not get freaked out about rushing off to see people or whatever.
4. I get to do what I want to do.
5. I don't have to share my stash with people who won't (or can't) repay.